Large electronic equipment generally comprises a plurality of circuit cards which make up the functional components of the equipment. Each of these circuit cards is plugged into a panel or backplane which provides the communication lines among the various circuit cards. In order to mechanically house and hold these cards in place, cabinets called "frames" have been used for many years.
FIG. 1 shows a typical frame for such circuit cards. Frame 100 has two metal sides 102, 104, and a metal top 106, floor 108, and back 110. The interior of this cabinet is subdivided into a plurality of shelves 112. Each shelf includes a number of plug-in card slots, which are then wired together on the backplane. Each shelf holds one or more circuit cards 114, depending upon the application. In the example of FIG. 1, there are power circuits 116 at the bottom of the frame and therefore very few circuits per shelf on the bottom. Alternatively, there are many circuit packs on the upper shelves.
Each circuit pack has a face plate 120, or stiffener, connected perpendicularly to the circuit pack on the end opposite the backplane. These face plates are commonly made of an electrically conductive metal such as aluminum to serve several functions. These face plates primarily serve as stiffeners to hold the circuit cards in a vertical orientation and keep them from flexing. Further, they provide a handle or grasping means to facilitate maintenance personnel removing and inserting the circuit cards. These face plates may also be used as a support for switches, labels, lights (i.e., system status, on/off, etc.) and other information (such as name or number of packs, etc.) regarding the state or condition of the circuit on the circuit card. It is currently standard in the art to provide gaps between the face plates on a particular shelf. These gaps allow easy insertion and removal of the circuit cards. Not having such gaps makes removal and insertion difficult, and greatly reduces tolerances for the backplane and the rack mounts of the circuit cards.
These gaps between the face plates, however, permit leakage of cooling air, electromagnetic radiation (EMR) both into and out of the cabinet, and electrostatic discharge (ESD). In order to meet standards for electromagnetic compatibility (EMC) from the front of a frame, prior art frames are equipped with a door 121. The circuit cards require thermal control which is normally provided by continuous air flow, and door 121 promotes air circulation by sealing the front of the frame. It is common to use large fans 122 at the bottom of a frame in order to circulate air up through the frame to an outlet 123 on top and thus cool it. For clarity, only a single fan is shown, but commonly a number are used. If air leaks through the front panel, as illustrated by the arrows 124, such cooling efficiency is greatly reduced. As well as adding cost and taking up valuable space, door 121 impedes access to circuit packs, because door 121 must be closed to maintain EMC compliance and thermal operating standards.
An objective is, therefore, to provide an electromagnetic radiation and susceptibility shield and air flow containment for thermal control without having to resort to a door.